Piping

ABSTRACT

The present invention relates to piping ( 1 ) for use in industrial activities, where the piping ( 1 ) has a specific geometry. In particular, the piping ( 1 ) is formed as a low amplitude helix, which causes fluid flowing through the piping ( 1 ) to swirl. This swirl flow provides a large number of advantages. Particular applications where the piping ( 1 ) can be used include petroleum production risers and flowlines, production tubing for downhole use in wells, pipelines for the transportation of fluids, static mixers, bends, junctions or the like, penstocks and draft tubes, reactors for chemical, petrochemical, and pharmaceutical applications, heat exchangers, cold boxes, incinerators and furnaces for waste disposal, static separators, and air intakes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 11/575,730, which constitutes the United Statesnational phase application of PCT/GB2005/003632, which has aninternational filing date of Sep. 21, 2005 and claims the prioritybenefit of United Kingdom Patent Application No. 0420971.4, filed Sep.21, 2004, the entire contents of each of which are hereby incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to piping for use in industrialactivities, which piping has a particular geometry.

BACKGROUND

Many industrial processes involve the transportation of fluids from onepart of a plant or machine to another, and this is routinely achievedthrough the use of piping. The fluid can also be treated during itspassage through the piping, for example by heating, irradiation,chemical reaction, and so on.

Pipes used in this way, and particularly those used to transport fluidsover long distances, are normally straight, in that their centrelinesare straight lines and the walls of the pipes are parallel to thecentrelines.

However, it has been found that alternative geometries for pipes can beemployed, which can provide a number of advantages over straight pipes.In particular, a pipe formed as a low-amplitude helix offers severalsignificant advantages over a straight pipe.

By “low-amplitude helix”, we mean that the pipe is formed such that itscentreline follows a substantially helical path, and that the amplitudeof the helix is equal to or less than one half of the internal diameterof the piping.

When fluid enters a piece of piping shaped as a helix in this way, swirlflow is established almost immediately. Swirl flow has a number ofadvantages over conventional flow. Turbulence, and associated pressurelosses (and energy losses) can be reduced. In addition, as a result ofmixing over the cross-section, the velocity profile of the flow acrossthe pipe is more uniform (or blunter) than it would be with flow in aconventional pipe, with the swirling fluid tending to act as a plunger,scouring the pipe walls.

It has been found that swirl flow is generally established across theentire width of the pipe within a few pipe diameters of the entry into alow-amplitude helix. Further, the secondary motion and mixing over thecross-section associated with the swirl flow results in considerablemass, momentum and heat transfer in fluid within the core, and betweenfluid at the walls of the pipe and fluid within the core.

The term “amplitude of the helix” as used here refers to the extent ofdisplacement of the centre line from a mean position to a lateralextreme. The amplitude is thus one half of the full lateral width of thehelical centre line. The cross-sectional area of the tubing is normallysubstantially constant along its length, but it can vary depending onthe particular characteristics required.

In low-amplitude helical piping of this type, where the amplitude of thehelix is less than one half of the internal diameter of the pipe, thereis a “line of sight” along the lumen of the piping. Even though the flowat the line of sight could potentially follow a straight path, it hasbeen found that it generally has a swirl component.

For the purposes of this specification, the term “relative amplitude” ofhelical piping is defined as the amplitude divided by the internaldiameter. Since the amplitude of the helical piping is less than orequal to one half of the internal diameter of the tubing, this meansthat the relative amplitude is less than or equal to 0.5. Relativeamplitudes less than or equal to 0.45, 0.40, 0.35, 0.30, 0.25, 0.20,0.15, 0.1 or 0.05 may be preferred. Smaller relative amplitudes providea better use of available lateral space, in that the piping is not muchwider overall than a normal straight pipe with the same cross-sectionalarea. Smaller relative amplitudes also result in a wider “line ofsight”, providing more space for the insertion of pressure gauges orother equipment along the piping. However, very small relativeamplitudes can in some circumstances lead to reduced secondary motionand mixing.

With higher Reynolds numbers, smaller relative amplitudes may be usedwhilst swirl flow is induced to a satisfactory extent. This willgenerally mean that, for a given internal diameter, where there is ahigh flow rate a low relative amplitude can be used whilst still beingsufficient to induce swirl flow. The angle of the helix (or pitch, wherethe pitch is the length of one turn of the helix, and can be defined interms of the internal diameter of the pipe) is also a relevant factor ininfluencing the flow. As with relative amplitude, the helix angle may beoptimized according to the conditions, and in particular the viscosity,density and velocity of the fluid being carried by the piping. The helixangle is preferably less than or equal to 65°, more preferably less thanor equal to 55°, 45°, 35°, 25°, 20°, 15°, 10° or 5°.

Generally speaking, for higher Reynolds numbers the helix angle may besmaller whilst satisfactory swirl flow is achieved, whilst with lowerReynolds numbers a higher helix angle will be required to producesatisfactory swirl. The use of higher helix angles for faster flows(with higher Reynolds numbers) will generally be undesirable, as theremay be near wall pockets of stagnant fluid. Therefore, for a givenReynolds number (or range of Reynolds numbers), the helix angle willpreferably be chosen to be as low as possible to produce satisfactoryswirl. In certain embodiments, the helix angle is less than 20°.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a length of tubing having a low-amplitude helicalgeometry.

DESCRIPTION

This tubing 1 has a circular cross-section, an external diameter D_(E),an internal diameter D_(I) and a wall thickness T. The tubing is coiledinto a helix of constant amplitude A (as measured from mean to extreme),constant pitch P, constant helix angle θ and a swept width W. The tubing1 is contained in an imaginary envelope 20 which extends longitudinallyand has a width equal to the swept width W of the helix. The envelope 20may be regarded as having a central longitudinal axis 30, which may alsobe referred to as an axis of helical rotation. The illustrated tubing 1has a straight axis 30, but it will be appreciated that the central axismay be curved, or indeed may take any shape depending on requirements.The tubing has a centre line 40 which follows a helical path about thecentral longitudinal axis 30.

It will be seen that the amplitude A is less than half the tubinginternal diameter D_(I). By keeping the amplitude below this size, thelateral space occupied by the tubing and the overall length of thetubing can be kept relatively small, whilst at the same time the helicalconfiguration of the tubing promotes swirl flow of fluid along thetubing. This also provides a relatively wide lumen along the tubing,which allows instruments, apparatus and the like to be passed down thetubing.

Use of low-amplitude helical piping can be beneficial to a large numberof processes involving the movement or transport of fluid through pipes,the mixing of fluids within pipes, heat and mass transfer into or out offluid within pipes, processes where deposition or contamination takesplace within pipes and processes where chemical reactions take placewithin pipes. This use is applicable to either gases or liquids as asingle phase or to a mixture of gases, liquids or solids in anycombination as a multiphase mixture. Use of such piping can havesignificant economic impact.

As an example, the reduction in turbulence and the associated reducedpressure drop provided by swirl flow will, under appropriate conditions,enable reduced pumping costs.

This can be significant in the distribution of hydrocarbons throughpipelines, including the crude oil and gas production process. Forexample, petroleum production risers and flowlines for use eitheronshore or offshore can include at least one portion which haslow-amplitude helical geometry. The low-amplitude helical geometryimproves the flow dynamics in the riser or flowline, in that it reducesflow turbulence through the flowline or riser, and thus reduces pressureloss.

The flowline or riser may be substantially vertical, substantiallyhorizontal, or have a curved geometry, including an S-shape or acatenary shape. The flowline or riser may be rigid or flexible, or anycombination of the two. The flowline or riser may be constructed fromany combination of materials, and may include strengthening rings.

Similarly, production tubing for downhole use within oil, gas, water, orgeothermal wells can use low-amplitude helical geometry. At least oneportion of a well will contain production tubing with low-amplitudehelical geometry. The benefits will include a reduction of flowturbulence, and reduced pressure loss.

Further, pipelines for the transportation of hydrocarbon can uselow-amplitude helical geometry, and will enjoy the benefits of reducedflow turbulence and reduced pressure loss. Of course, pipelines for thetransportation of other fluids, such as potable water, waste water andsewerage, slurries, powders, food or beverage products, or indeed anysingle phase or multiphase fluids, can also have a low-amplitude helicalgeometry and enjoy the same benefits.

Another area where the reduced pressure drop is of particular benefit isin the context of penstocks and draft tubes for hydropower applications.Reduced pressure loss will lead to increased power generation output,and even a small reduction in pressure drop can lead to a very largeincrease in power output over the life of the plant.

A reduced pressure drop is also important in the distribution of steamaround power stations and other industrial plant. It is also importantfor the operation of chemical reactions where the pressure needs to bemaintained at the lowest possible level to improve yields, includingprocesses operated under vacuum, such as the production of olefins bypyrolysis and the production of styrene from ethyl benzene.

Mixing within pipes is important in many industries including thechemical, food, pharmaceutical, water and oil industries. It is oftenimportant that a small amount of active chemical is uniformlydistributed in a large mass of other material. In some instances, thisis known as dosing. Examples would be the addition of antioxidant to avariety of materials and foods, and the addition of chlorine or alkalito drinking water. The low-amplitude helix, because it deliversintrinsically good mixing, can reduce the amount of active chemicalneeded to ensure a sufficient concentration to achieve the desiredpurpose, and can ensure the absence locally of unacceptably high (orlow) concentrations of additives.

Mixing is also important where it is required to bring together two ormore large streams of fluids and ensure they do not remain separate.Mixing is furthermore important where it is beneficial to retain thefluid as a stable mixed phase (to prevent unwanted phase separation).This is important in the production of crude oil and gas, where theseparation of gas creates slugging which reduces the capacity ofpipelines and raises the expense of the operation. Indeed, a furthermajor benefit of the use of low-amplitude helical geometry in petroleumproduction risers and flowlines, production tubing for downhole use, andpipelines for transportation of hydrocarbons and other fluids is thereduction of slug flow. The improved phase mixing is also significant inpipelines, as it tends to keep gas or air in the fluid, rather thenhaving it collecting at the high points of the pipe and possibly causingairlocks.

Mixing is also important in the transport of solids by a liquid, as inthe transport of sewage or the transport of minerals by pipeline inminerals extraction processes, to prevent the solids from settling out.This reduction of sedimentation (and of mineral and/or hydrocarbonprecipitation) is also significant for petroleum production risers andflowlines, and production tubing for downhole use. Reduction ofsedimentation is also important in hydropower applications. In addition,in petroleum production risers and flowlines, and production tubing fordownhole use, the improved mixing reduces the risk of water drop-out.

As an example, static mixers for chemical dosing, and food, chemical,petrochemical and pharmaceutical processing, can use low-amplitudehelical geometry. The benefits will include increased cross-mixing, andreduced blocking by sediment or precipitate. In addition, as discussedabove, the low-amplitude helical geometry will also give a reduced mixerpressure-loss. Further, since there is a “line of sight” lumen along thelow-amplitude helical portion, and there are no baffle plates or vanesas are commonly found in conventional mixers, there is increased ease ofcleaning. These benefits will result in reduced maintenance and wear.

Further, the improved mixing (in particular thermal mixing) and reducedpressure loss which can be achieved using low-amplitude helical geometryis particularly beneficial in heat exchangers in power stations,refrigeration cold boxes, air separation cold boxes, and the like.

Low-amplitude helical piping can also be used to ensure complete mixingof components prior to reaction. This will ensure that reaction takesplace more completely and that materials are used efficiently. Typicallythis would involve mixing gaseous or liquid reactants prior to passingthem over a catalyst. However, it is specifically envisaged that thiscould be used for mixing fuel and air prior to passing them to aninternal combustion engine. This would improve the efficiency of theinternal combustion process and reduce the amount of unburnt orpartially combusted fuel and fine solids passing to the atmosphere. Thislast improvement will also reduce the demand on and thus improve theperformance of the catalytic converter downstream of internal combustionengines used in road transport.

Because the low-amplitude helical piping ensures helical (swirl) flowwithin pipes and generates a blunter velocity profile, the rate anduniformity of heat transfer to and from the fluid inside the pipe can beimproved. In normal flow, the fluid at the centre of the pipe movesconsiderably faster than the fluid near the walls of the pipe, and so ifthe pipe is heated, the fluid near the walls will be heated to a greaterdegree than the fluid near the centre of the pipe.

However, as swirl flow has a blunter (and thus more uniform) velocityprofile, it is less likely that parts of the fluid will be over- orunder-heated, causing unwanted effects. The low-amplitude helical pipingallows the same heat to be transferred with a lower differentialtemperature between the inside and the outside of the pipe.

This can be os particular benefit when a component is added to a fluidand treated in some way (such as heating). With poor mixing, the part ofthe mixture which is travelling quickly will be undertreated, and thepart of the mixture which is travelling slowly will be overtreated;however, with the very good mixing provided by the low-amplitude helicalgeometry, this can be avoided, and more uniform treatment achieved.

This can be of serious economic benefit in furnaces such as olefincracking furnaces, preheating furnaces for refinery thermal crackers orvisbreakers, transfer line exchangers in olefin plants, heat exchangersin power stations, cold boxes for industrial refrigeration units, coldboxes for air separation units and refrigeration units generally.

The blunt velocity profile is also beneficial in hydropowerapplications. Turbines tend to work better when the velocity profile isblunter, and so use of the low-amplitude helical portions in hydropowerapplications can improve efficiency in this way. Additional advantagesof swirl flow in the context of hydropower applications include reducedcavitation and reduced pipe stresses.

In addition, the “plunger” aspect of the swirl flow generated by thelow-amplitude helical piping can provide significant economic benefitsto those processes taking place in pipes where the deposition of finesor other solid particles on the inside wall of the pipe creates abarrier to heat transfer, or contaminates the fluid flowing through it,or reduces the flow of fluid through the pipe. Such fines or other solidparticles can be present in the fluid, or can be created by a chemicalreaction between the components of the fluid.

The use of low-amplitude helical piping is expected to significantlyreduce such solid deposition on the internal walls of the pipe, thusextending its operating life before cleaning, reducing the amount ofheat necessary, and reducing the pressure drop compared to the fouledpipe. Examples of where this effect could be economically significantare the transport of solids in liquid pipelines, and also the productionof olefins by pyrolysis, where the deposition of coke on the inside ofthe furnace coils requires them to be taken out of service for cleaning(typically every 20 to 60 days). A similar effect occurs in otherfurnaces such as the preheat furnaces for refinery processes.

Further, the blunt velocity profile and the “plunger” aspect isextremely useful in the context of batch processing, which is common inpharmaceutical and food processing. Because of the blunt velocityprofile, the axial dispersion of batches can be reduced and the peakconcentration achieved much earlier than for conventional arrangements.These features are particularly beneficial if the batch sizes are small.In addition, the “plunger flow” helps to remove traces of a firstcomponent from the pipe walls after switching to a second component,which helps reduce the chance of contamination in batch processing. Thetime required to wash out the system may at least be reduced along withthe quantity of fluid required to perform the washing-out.

Using low-amplitude helical piping can also have material economicsignificance where chemical reactions take place in pipes or tubes. Thecombination of improved mixing and more uniform heat transfer willimprove yields and encourage the completion of reactions (includingcombustion). Improving yields will also reduce downstream separationcosts. Example processes where this would be important include olefinproduction and similar gas phase reactions, such as the cracking oftoluene to form benzene, and conversion of butene-1 to butadiene. Wheresuch reactions involve the production of more than one molecule ofproduct for each molecule of feedstock, the lower pressure drop in thereactor and its downstream pipework which can be achieved through theuse of low-amplitude helical piping provides an additional benefit fromthe lower average pressure, because it will reduce the possibility ofthe product molecules recombining to form the feedstock or otherunwanted byproducts. In addition, the use of low-amplitude helicalgeometry in reactors for chemical, petrochemical, and pharmaceuticalapplications, can lead to decreased carbon deposition in the reactortubes, which is of particular importance in the petrochemical industry.

The improved mixing and more uniform heat transfer will also encouragethe completion of combustion reactions without a large amount of excessair (over that required by the stoichiometry of the reactions). This isparticularly important for incinerators or waste disposal furnaces,where it is necessary to ensure complete reaction to prevent chemicalsand/or particles deleterious to the environment and human healthescaping into the atmosphere. This could be prevented and completecombustion ensured by passing the combustion gases, while still hot,through a section of piping formed as a low-amplitude helix beforepassing them to the atmosphere. The generation of swirling flow throughthe furnace will increase the rate and efficiency of combustion, and theremoval of waste.

When used with flows that include two or more different phases, thelow-amplitude helical portion can furthermore be used to separate “inline” a mixture of fluids having different densities. The swirlingcreated by the helical flow tends to displace higher density componentsof the mixture towards the tube walls and lower density componentstowards the centreline, as a result of the centrifugal effect. By meansof suitable arrangements, higher (or lower) density components can bedrawn off, leaving the remaining component present in increasedconcentration. The process can be repeated using further similar in-linestatic separators. This separation can be used to remove gases fromliquids, and can therefore be used to help reduce slugging in thepetrochemical industry in particular.

An approach similar to this can be used to either increase or decreasethe concentration of particles in a flowing fluid. This will be achievedby drawing off fluid either from the vicinity of the tube centreline orfrom near to the tube walls.

In addition, the swirl flow caused by the low-amplitude helical portioncan be used to remove particulate matter from a flow. This is ofparticular importance in, for example, air intakes. Air intakes are usedin a great many situations where air is required, and in particular onvehicles where air is required for combustion and/or cooling. Helicopterair intakes in particular usually need dust separators, to prevent dustreaching the engine, but the swirl flow generated by the low-amplitudehelical geometry can be used to separate the dust from the airflowwithout the need for separate filters.

Further, it has been found that swirl flow caused by a low-amplitudehelical portion continues for some distance in a straight pipedownstream of the section. Thus, a section of the low-amplitude helicalpiping can be inserted upstream of structures such as bends, T- orY-junctions, manifolds, and/or changes of conduit cross-section, wherethe swirl flow generated by the low-amplitude helical portion wouldsuppress flow separation, stagnation and flow instability, with benefitto pumping costs and corrosion and wear in pipes. The particularbenefits of the swirling flow at the bend, junction or the like will bereduced flow separation, leading to reduced pressure loss, reducedsedimentation and precipitation, reduced cavitation, and increased flowstability. Low-amplitude helical geometry pipes positioned before bendswill also reduce particulate erosion within pipe bends, which can be ofparticular benefit with regard to fuel feed to power stations.

It will thus be clear to the skilled person that piping with alow-amplitude helical geometry can provide many advantages in a largenumber of situations.

1. A reactor comprising an incinerator or a waste disposal furnace, thereactor further comprising a reactor tube, characterized in that thereactor tube has a centerline (40) which follows a substantially helicalpath, wherein the amplitude (A) of the helix is equal to or less thanone half of the internal diameter (D_(I)) of the tube so as to provide aline of sight along the lumen of the tube.
 2. A reactor as claimed inclaim, 1, wherein the tube has a substantially circular cross-sectionand an external diameter (D_(E)) and wherein the tube is contained in animaginary envelope (20) which extends longitudinally and has a width (W)equal to the swept width of the tube, the width of said envelopedefining the lateral space occupied by the tube and being greater thanthe external diameter (D_(E)) of the tube.
 3. A reactor as claimed inclaim 2, wherein the envelope has a central longitudinal axis (30) aboutwhich the helical centerline (40) of the tube follows a helical path,and wherein the central longitudinal axis is straight.
 4. A reactor asclaimed in claim 2, wherein the envelope has a central longitudinal axis(30) about which the helical centerline (40) of the tube follows ahelical path, and wherein the central longitudinal axis is curved.
 5. Areactor as claimed in claim 1, wherein the amplitude (A) of the helix isless than or equal to 0.4 of the internal diameter (D_(I)) of the tube.6. A reactor as claimed in claim 1, wherein the angle of the helix isless than or equal to 55°.
 7. A reactor as claimed in claim 1, whereinthe reactor tube is a tube through which hot combustion gases are passedin use.
 8. A method of using a reactor comprising an incinerator or awaste disposal furnace and as claimed in claim 1, for combustionreactions.
 9. Petroleum production risers and flowlines for use eitheronshore or offshore, using low-amplitude helical geometry. 10.Production tubing for downhole use within oil, gas, water, or geothermalwells, using low-amplitude helical geometry.
 11. Pipelines for thetransportation of hydrocarbon, potable water, waste water and sewerage,slurries, powders, food or beverage products, or any single phase ormultiphase fluids, using low-amplitude helical geometry.
 12. Staticmixers for chemical dosing, and food, chemical, petrochemical andpharmaceutical processing, using low-amplitude helical geometry. 13.Bends, junctions or the like, involving a length of low-amplitudehelical geometry pipe upstream of a planar bend or similar, which willgenerate swirling flow around the bend.
 14. Penstocks and draft tubesfor hydropower applications, using low-amplitude helical geometry. 15.Reactors for chemical, petrochemical, and pharmaceutical applications,using low-amplitude helical geometry.
 16. Heat exchangers in powerstations, refrigeration cold boxes, and air separation cold boxes, usinglow-amplitude helical geometry.
 17. Incinerators and furnaces for wastedisposal, using low-amplitude helical geometry.
 18. Static separatorsfor use in industrial processes where there is flow of a mixture offluids having different densities, using low-amplitude helical geometry.19. Air intakes, using low-amplitude helical geometry.
 20. An intake foran internal combustion engine, using low-amplitude helical geometry.